1. Field of the Invention
The present invention relates to a substrate laminating apparatus and a substrate laminating method used for laminating an optical substrate to a display device, for example, and to a stereoscopic display device.
2. Description of the Related Art
In accordance with the recent needs for sophisticated functions of display devices, there has been used a peculiar display device capable of providing stereoscopic image display and the like in which an optical substrate such as a lenticular lens substrate, a parallax barrier substrate, or a liquid crystal lens substrate is combined with a display panel that uses an electro-optical element such as a liquid crystal or an organic EL (electroluminescence).
As an example of such display device, a display device using a lenticular lens substrate will be described. FIG. 19A is a schematic perspective view of the lenticular lens substrate, and FIG. 19B is a schematic chart showing a structural example of the display device using the lenticular lens substrate and a stereoscopic display method.
As shown in FIG. 19A, one of the surfaces of the lenticular lens substrate 50 is constituted with a plane face and the other surface is constituted with cylindrical lenses 51. The cylindrical lens 51 has a cylindrical surface and a semicircular sectional shape, and a plurality of the cylindrical lenses are continuously provided in an extended manner in an x-direction and a parallel direction.
As shown in FIG. 19B, a left-eye pixel 65a and a right-eye pixel 65b are alternately disposed on a display panel 64 by corresponding to the focal points of each of the cylindrical lenses 51. When the left-eye pixels 65a and the right-eye pixels 65b are driven according to prescribed signals by a driving circuit, not shown, a left-eye image is formed in a left-eye region 70a and a right-eye image is formed in a right-eye region 70b, respectively, by the cylindrical lenses 51. This makes it possible for an observer to recognize a stereoscopic image. Needless to mention, it is also possible to display normal two-dimensional images by driving the left-eye pixels 65a and the right-eye pixels 65b with a same signal.
Further, as a display device using a lenticular lens substrate, there is a plural-image simultaneous display device which simultaneously displays a plurality of images. Through distributing different images for observing directions by the cylindrical lenses with the same method for achieving stereoscopic display described above, this display device becomes capable of simultaneously displaying images different from each other for a plurality of observes.
With such display device using the lenticular lens substrate, it is required to mount the lenticular lens substrate on the display panel with high precision in order to achieve high-quality stereoscopic display or plural-image simultaneous display. Particularly, for high-definition display devices loaded on recent terminal devices, it is required to achieve lamination with high precision in the order of μm which has not been required conventionally.
In order to achieve the lamination precision in the order of μm, it is necessary to form a mark of the optical substrate and a mark of the display panel in the order of μm, respectively. However, in general, it is difficult to form the marks with the precision of μm at the time of manufacturing the optical substrates by machining.
As an example of a lens mark forming and mark reading method for overcoming such issue, the method depicted in Japanese Unexamined Patent Publication 2012-013933 (Patent Document 1) will be shown (FIG. 20). As a mark for reading out the positional information of the lenticular lens substrate 50, at least one non-periodical flat part 54 with which the period of the cylindrical lenses changes is provided at an end part in a lens pitch direction as shown in FIG. 20A. FIG. 20B is an example of an image acquired by irradiating light to a contact part between the lenticular lens substrate 50 and a substrate head 58 and capturing the reflection light thereof. If a specific positional relation such as the non-periodical flat part 54 is clear, it is possible to read the pitch of a specific position on the lenticular lens substrate 50. In this manner, the positional information of the lens is read out from the luminance distribution of the reflection light, the panel mark of the display panel is captured via an another camera, and the positions are aligned in the manner of indirect alignment. In the meantime, in a case of direct alignment with which the panel mark of the display panel is read out via the lenticular lens substrate, the position of the panel mark is observed by being changed by the refraction effect generated by the lenticular lens. Thus, in regards to securing the precision, the indirect alignment is more useful than the direct alignment.
Further, in a case where the display panel and the optical substrate are constituted with highly rigid materials, air bubbles tend to be mixed at the time of lamination since rigid bodies are to be laminated. For preventing the mixture of air babbles, it is known to laminate the both under a reduced pressure that is lower compared to an atmospheric pressure as depicted in Japanese Unexamined Patent Publication 2012-133098 (Patent Document 2). As the lamination materials, an adhesive film called OCA (Optically Clear Adhesive) and an adhesive called OCR (Optical Clear Resin) are used in general.
In order to achieve the highly precise lamination with such reduced-pressure laminating apparatus, first of all, used is a vacuum chamber having high rigidity in which a door valve for moving in and out the display panel and the optical substrate and other part than the opening part called a gate valve are formed as a unified structure. Secondly, mechanism components having a driving system such as highly precise XYZ-axis guide and a linear scale are used in a camera that is used for measuring the positions of an upper table and a lower table and for measuring the positions of the display panel and the optical substrate.
Now, the outline of highly precise lamination done by the reduced-pressure laminating apparatus of the related technique will be described based on paragraphs 0012 to 0014 and the flowchart of FIG. 4 shown in Patent Document 2. In a vacuum chamber, an upper table and a lower table are disposed in parallel to be facing with each other vertically with a space provided therebetween. The door valve of the vacuum chamber is opened, a display panel and an optical substrate are inserted inside the vacuum chamber, either one (upper substrate) of the display panel and the optical substrate is held to the upper table by having its lamination surface facing downwards, and the other one (lower substrate) is held on the lower table by having its lamination surface facing upwards. When the upper and lower substrates are completely placed inside, the door valve is closed, and the inside of the vacuum chamber is evacuated. Further, in a state where the upper and lower tables are facing each other vertically with a space provided therebetween, alignment marks provided, respectively, on the optical substrate and the display panel, are read out by a plurality of position measurement cameras, and positions of the upper substrate and the lower substrate are aligned by a horizontal-direction (XYθ direction) movable mechanism that is provided on the lower table. Subsequently, the upper table is brought down by a driving motor, and the upper and lower substrates are laminated. The laminated substrates are sent out from the vacuum chamber by a transport mechanism through opening the gate valve of the vacuum chamber.
There is no specific technique shown in Patent Document 2 as a technique for reading out the alignment marks provided on the optical substrate and the display panel, respectively, by using the position measurement camera. However, for example, there are a technique (FIG. 4 of JP 4330912 B (Patent Document 3)) with which a camera is disposed on the outer side (atmospheric pressure side) of a vacuum chamber and alignment marks of the upper substrate and the lower substrate inside the vacuum chamber are captured through a window that is opened through the vacuum chamber and a technique (JP 4192181 B (Patent Document 4)) with which a vacuum-resistant camera is provided inside the vacuum chamber, and alignment marks are captured under a vacuum environment.
Further, devices for performing lamination by using an upper and lower vacuum chambers and manufacturing methods thereof are depicted in Japanese Unexamined Patent Publication 2008-286886 (Patent Document 6), Japanese Unexamined Patent Publication 2010-020068 (Patent Document 7), and Japanese Unexamined Patent Publication 2009-258582 (Patent Document 8).
However, in a case where lens lamination is performed by using the methods of the related techniques described above, there are following issues to be raised.
Patent Document 2 discloses a reduced-pressure laminating apparatus which has a vacuum chamber and laminates a display panel and an optical substrate under a reduced pressure. For performing such lamination of an optical sheet constituted with a lenticular lens substrate and a panel substrate, following structures cam be considered when the mark reading method (indirect alignment) shown in Patent Document 1 is employed.
The optical sheet is held on the upper table by having its lamination surface facing downwards, and the panel substrate is held on the lower table by having its lamination surface facing upwards. After evacuating inside the vacuum chamber, a position measurement camera is disposed under an alignment mark of the optical sheet through inserting the position measurement camera into a gap between the upper table and the lower table disposed in parallel with a space provided therebetween. Further, light is irradiated to a contact part between the upper substrate and the upper table, and the reflection light from the alignment mark is captured and read out. Then, the alignment mark of the display panel is read out, and the positions of the upper substrate and the lower substrate are aligned by a horizontal-direction (XYθ direction) movable mechanism that is provided on the lower table. Finally, the upper table is brought down by a driving motor, and the upper and lower substrates are laminated tightly.
The point of this structure is to use the vacuum-resistant camera shown in Patent Document 4 as the position measurement camera, to insert the position measurement camera into the space between the upper and lower tables, and to capture and read out the reflection light of the alignment mark. However, there are following issues with the mechanism constituted with such structure.
The camera that can bear the vacuum environment shown in Patent Document 4 used as the position measurement camera requires special exterior members as well as wirings such as a camera casing formed with stainless steel, a connector, and a jacket that covers the connector. Thus, such camera is a more complicated structure than a regular camera used in an atmospheric pressure, so that it is expensive. Therefore, the cost is increased further when a plurality of those cameras are to be used.
Further, because of the structure with which the position measurement camera is inserted into the space between the upper and lower tables, it is necessary to add a highly precise XY transport mechanism within the vacuum chamber for moving the position measurement camera in the horizontal direction (XY). It is more difficult for the transport mechanism used in vacuum to radiate the heat compared to the transport mechanism used in an atmospheric pressure, so that the cost for securing the heat radiation performance and the heat resistance performance is more increased.
Further, the moving stroke of the camera transport mechanism is greater at least than the plane size of the upper table. It is because the camera needs to be evacuated from the upper table so that the camera does not become an obstruction when the upper table moves up and down in a laminating action. Thereby, the transport mechanism whose plane size is larger than that of the upper table is structured in the periphery of the upper table. Thus, the vacuum chamber that houses the transport mechanism becomes considerably larger than the case of Patent Document 2 described above. The increase in the size of the vacuum chamber leads to the increase in the size and weight of the entire laminating apparatus. Thus, it is required to increase the size of the device frame and to take a measure for increasing the rigidity, so that not only the cost but also the installment space is increased.
As a measure thereof, there is considered following Improvement Plan 1. This is a plan which uses the camera generally used in an atmospheric pressure as the position measurement camera and employs the transport mechanism that moves the position measurement camera in an atmospheric pressure as shown in FIG. 20 and FIG. 21 of WO 2010/026768 (Patent Document 5). This Improvement Plan 1 will be described in the followings.
Inside the vacuum chamber, the upper table and the lower table are disposed in parallel by facing with each other vertically with a space provided therebetween. By the side of the vacuum chamber, provided is a camera transport mechanism constituted with a scalar-type robot, an XY parallel-direction direct robot, or the like in which a plurality of position measurement cameras are provided in the tip end of an arm-type supporting body. The door valve of the vacuum chamber is opened, a display panel and an optical substrate are inserted inside the vacuum chamber, the optical substrate is held on the upper table by having its lamination surface facing downwards, and the panel substrate is held on the lower table by having its lamination surface facing upwards. When the upper and lower substrates are completely placed inside, the camera transport mechanism is inserted from the opening part of the door valve in a state where the upper and lower tables are placed to face with each other with a space therebetween, and the position measurement camera is disposed under the alignment mark of the optical substrate. Further, light is irradiated to the contact part between the upper substrate and the upper table, and the reflection light from the alignment mark is captured and read out. Then, the alignment mark of the display panel is read out. When reading of the alignment marks is completed, the camera transport mechanism is drawn out from the opening part of the door valve, and the position measurement camera is taken out to the side of the vacuum chamber. Subsequently, the door valve is closed, and the inside of the vacuum chamber is evacuated. Then the positions of the upper substrate and the lower substrate are aligned by a horizontal-direction (XYθ direction) movable mechanism that is provided on the lower table. After the position alignment, the upper table is brought down by a driving motor, and the upper and lower substrates are laminated. The laminated substrates are sent out from the vacuum chamber by a transport mechanism through opening the gate valve of the vacuum chamber.
The point of Improvement Plan 1 is to provide the camera transport mechanism constituted with a scalar-type robot, an XY parallel-direction direct robot, or the like in which a plurality of position measurement cameras are provided in the tip end of an arm-type supporting body by the side of the vacuum chamber and to read out alignment marks in an atmospheric pressure. Thereby, it becomes unnecessary to employ the above-described vacuum-resistant camera and the transport mechanism used in vacuum, so that a certain effect can be expected to address the increase in the cost and expansion in the installment space regarding those.
However, with Improvement Plan 1, it is difficult to have the lamination precision within the order of μm. That is, the arm-type supporting body having the position measurement cameras in the tip end thereof is formed in a cantilever structure having its fulcrum on the outside of the vacuum chamber. Therefore, position shift and defocusing are generated in the position measurement camera by the oscillation of the surroundings transmitted to the camera transport mechanism, so that the alignment precision is deteriorated.
Based on the above, the reduced-pressure laminating apparatus shown in Patent Document 2 still faces issues in regards to the increase in the cost, expansion in the installment space, deterioration in the lamination precision, and the like, for laminating the optical sheet constituted with the lenticular lens substrate and the display panel substrate.
In the meantime, Patent Document 1 discloses a lens mark forming and mark reading method for an optical sheet constituted with a lenticular lens substrate as well as a laminating method of an optical sheet and a display panel. As shown in paragraph 0054, FIG. 1C, and FIG. 8B of Patent Document 1, the optical sheet and display panel laminating method is to laminate the optical sheet constituted with the lenticular lens to the display panel by tilting the sheet holding head with respect to the display panel. However, as the lamination started from the end part proceeds, the contact angle between the sheet holding head and the display panel becomes smaller gradually. Thus, there is a risk of having air bubbles inserted immediately before completion of the lamination, and it is expected that the rate of having the air bubbles inserted therein becomes greater as the optical sheet becomes larger.
Further, also disclosed in Paragraphs 0061 to 0063 and FIG. 1 of Patent Document 1 is a method which laminates the optical sheet to the display panel continuously from the end part of the optical sheet towards the end part on the opposite side by having the held optical sheet to be in contact with the display panel by using a sheet holding head having an arc-shape holding face and rotating the rotation shaft of the sheet holding head while relatively moving the display panel or the rotation shaft itself to synchronize with the rotation. With this method, the contact angle between the optical sheet and the display panel becomes always constant from the start of lamination to the end. Thus, it is expected that there is no risk of having air bubbles inserted immediately before completing the lamination as mentioned above. However, while a film-sheet type optical sheet formed with a material that can be bent smoothly without hindrance can be held to the arc-shape holding face, it is difficult to hold the optical sheet formed with a highly rigid material. For example, it is difficult with this method to laminate an optical sheet constituted with a lenticular lens substrate having a transparent plate such as glass as a base member.
Thus, there is considered following Improvement Plan 2 in which a vacuum chamber and a vacuum evacuation system are added to the sheet holding head and the panel stage shown in a first exemplary embodiment of Patent Document 1, and lamination is performed in a reduced pressure that is lower than an atmospheric pressure.
Specifically, the vacuum chamber is formed as a divided structure constituted with a pair of vertically divided cubic vacuum chambers, the sheet holding head is disposed inside of the upper chamber (upper vacuum chamber) that is one of the vacuum chambers, the panel stage is disposed inside the lower chamber (lower vacuum chamber) that is the other vacuum chamber, and a vacuum evacuation system is provided on the side face of the lower vacuum chamber. Further, as the lamination steps, a step of forming a closed space as a vacuum chamber by a contact between the upper vacuum chamber and the lower vacuum chamber when bringing the sheet holding head and the panel stage to become close vertically and then reducing the pressure inside the vacuum chamber (surroundings of the sheet holding head and the panel stage) by evacuation before performing lamination is added to the step of laminating the optical sheet to the display panel (see step 106 of paragraph 0033 of Patent Document 1).
With this Improvement Plan 2, it is expected to become capable of laminating the above-described optical sheet constituted with a lenticular lens substrate having a transparent plate member as a base material. Further, the inner size of the added vacuum chamber simply needs to be slightly larger than the plane size of the sheet holding head and the panel stage. Thus, it is estimated that expansion of the installment space by employing Improvement Plan 2 is relatively small.
However, the vacuum chamber added in Improvement Plan 2 is formed in a divided structure being divided into two vertically. Thus, compared to a unified-structure vacuum structure, there is such an issue in terms of the structure that the rigidity of the parts divided into two vertically is deteriorated. That is, through providing a piping apparatus of the vacuum evacuation system on the side face of the lower vacuum chamber, the compression force by the atmospheric pressure at the time of reducing the pressure works as a shear force on the side face (horizontal direction) of the lower vacuum chamber. This causes deformation of the lower vacuum chamber. The deformation of the lower vacuum chamber causes position shift of the panel stage. Further, the shear force deteriorates the alignment precision of the horizontal transport mechanism of the panel stage. Particularly, when the vacuum evacuation direction is roughly consistent with the direction along which the lamination precision is required, the lamination precision is deteriorated by vacuum evacuation before and after a curing process of an adhesive such as OCR, for example.
Further, in a case of indirect alignment shown in Patent Document 1, it is necessary to individually capture the images of each of the marks of the optical substrate and the display panel. For example, in a case where the imaging camera exists at a fixed position when capturing the image of the optical substrate as shown in FIG. 20B of the current Specification, it is necessary to provide a step of capturing the image while moving the optical substrate and to provide a highly precise transport mechanism in order to capture marks at a plurality of points within the optical substrate. This leads to the increase in the size of the device frame due to the added transport mechanism, so that not only the cost but also the installment space is increased.
Further, regarding the transport mechanisms, there necessarily exits shift (error) in the position called alignment precision in each of the mechanisms. It means that the position shift (error) of the transport mechanism is accumulated as the number of the transport mechanisms associated with the lamination precision is increased so that the lamination precision becomes deteriorated gradually. The laminating apparatus requires lamination precision in the order of μm. Therefore, it is desired to achieve the device structure having the reduced number of transport mechanisms as much as possible in order to implement and maintain the precision.
In Patent Documents 6, 7, and 8, shown is a structure using a direct alignment method, which includes a means for capturing images of marks on the substrate in a state where an optical substrate and a display panel are placed in parallel by facing with each other with a space provided therebetween. With this method, when the optical substrate is employed as the substrate as described above, the position of the panel mark is observed by being changed by a refraction effect of the optical elements (lenticular lenses, for example) on the optical substrate. Thus, this method is inferior to indirect alignment in regards to securing the precision.
Further, with the techniques disclosed in Patent Documents 3, 6, 7 and the second exemplary embodiment of Patent Document 8, it is required to provide a window of light-transparent glass opened through a vacuum chamber in accordance with the mark capturing position. Thus, when changing the panel size, it is necessary to add the light-transparent window and modify the size of the window so that the cost is increased. In the first exemplary embodiment of Patent Document 8, disclosed is a structure with which no light-transparent glass is provided in a vacuum chamber while providing a camera inside the vacuum chamber. However, as described in Patent Document 4, the camera that can bear the vacuum environment is expensive. Further, the third exemplary embodiment of Patent Document 8 shows a structure with which lamination is performed under the vacuum environment. However, when an adhesive film called OCA is used as a lamination material, there is a risk of having air bubbles inserted between the optical substrate and the display panel as described above.
Further, in the technique disclosed in Patent Document 7, the lens pitch direction and the vacuum evacuation direction are the same as shown in FIG. 4 thereof. However, the lens pitch direction is the direction along which the lamination precision is required. Therefore, with this technique, the lamination precision is deteriorated by the vacuum evacuation as described above.
It is therefore an exemplary object of the present invention to provide a substrate laminating apparatus and a substrate laminating method capable of making it possible to perform lamination with high precision when laminating two substrates while saving the cost and space, and to provide a stereoscopic image display device of high image quality, which is manufactured by using the substrate laminating apparatus and the substrate laminating method.